Stainless alloys containing gallium



United States Patent 3,134,670 STAINLESS ALLQYS CONTAlNlNG GALLIUM EmilM. Prosen, Bala-Cynwyd, Pa, assignor to Nobiliurn Products, Inc,Philadelphia, Pin, a corporation of Pennsylvania No Drawing. Filed May18, 1961, Ser. No. 110,857 2 Claims. (Cl. 75-171) The present inventionrelates to stainless base metal alloys and aims to provide certainimprovements therein.

By stainless base metal alloy is meant, an alloy containing asubstantial percentage of chromium and a substantial percentage of atleast one of the metals selected from the group consisting of iron,nickel, and cobalt and which is corrosion resistant and will retain ahigh luster or polish imparted thereto. Such alloys usually contain intheir formulations one or more of the elements: manganese, molybdenum,tungsten, vanadium, silicon, titanium, aluminum, copper, carbon,phosphorous, sulphur, and possibly others in small amounts for impartingsome special property or characteristic to the alloy. Stainless steelsand non-ferrous alloys for use in the manufacture of cast dentures arealloys of the character to which the present invention relates.

For about twenty years the better known cobalt-chromium dental alloyshave been pretty much on a par. Chemical analysis and microstructureshave varied in minor respects, and these differences have yielded alloyswhich varied to some degree in propertiesthere were small ditferences,for example, in surface hardness, in resistance to bending, in tensilestrength, in corrosion resistance, etc. Considering the field of the topalloys, not one of them Was so outstanding as to be instantly anduniversally recognized as the best.

The primary object of the present invention is to modify the formulationof known stainless base metal alloys and to provide special formulationsof such alloys which will possess a silvery luster, gleam, andreflectivity greater than has been heretofore obtainable by thestainless base metal alloys.

A further object of the invention is to improve the workability ofstainless base metal alloys so that machining, grinding, and polishingthereof is rendered more facile.

A further and more specific of the invention, not to provide dentalcasting alloys which will possess ease of flow in the casting ofdentures, a bright silvery luster when polished, and a resiliencyessential in cast dentures.

The foregoing and other objects of the invention, not specificallyenumerated, I accomplish by incorporating from 0.01 to of gallium informulations of stainless base metal alloys of the character specified.

The addition of gallium in amounts from 0.01 to 10% to conventionalstainless steels and to stainless base metal alloys such for example asare discolsed in my prior US. Patent No. 2,128,847 primarily adapted foruse in the manufacture of cast dentures imparts to such alloys 21 brightsilvery luster when polished, renders the machining, grinding andpolishing of the resulting alloy more facile without materiallyadversely affecting the tensile strength or the hardness of the alloy.Although the addition of gallium lowers the melting point slightly, itis primarily added to promote a fine grain structure in the alloy andease of flow at casting temperatures.

In all alloys to which the present invention relates, chromium is theelement which imparts the stainless and corrosion resistant properties.In stainless steels, chromium must be present in amounts not below 8.5%nor appreciably above 26%. In such alloys part of the iron may bereplaced by nickel, cobalt, molybdenum, tungsten or vanadium. in denturecasting alloys chromium may be present in amounts up to 35% and suchalloys usually 3,134,570 Patented May 26, 1964 contain at least one ofthe elements selected from the group consisting of nickel, cobalt, iron,molybdenum, tungsten, and vanadium, and wherein the combined elements ofsaid group may vary between 6570%.

Since the composition of stainless steels and of corrosion resistancedenture casting alloys vary within relatively Wide limits I havedetermined that the addition of 0.01-10% gallium will produce in theresulting alloy the desired bright silvery luster when polished, andease of working, grinding, and polishing. I have also found that indental casting alloys the presence of gallium in an amount as low as0.01% will impart the characteristic of a bright silvery luster whenpolished and as the percentage of gallium is increased, the workabilityand fineness of grain of the alloy are increased and its hardness isreduced. Accordingly, since the present cost of gallium is about $25 pergram, the amount used in the formulation of an alloy should be governedby the use of the minimum quantity which will produce the desiredcharacteristics of a bright silvery luster when polished and ease ofworkability.

Where stainless steel is fabricated for use as tableware, cutlery, Watchcases and other articles of manufacture requiring a high lusterresembling polished silver, I have found that from 0.012% of galliumwhen added to a stainless steel composition normally intended for suchuses will impart to such stainless steels a bright silvery luster whenpolished.

Where non-ferrous corrosion resistant alloys, are intended for use inthe manufacture of denture castings I have found that from 0.01-1% ofgallium when added to alloys now conventionally used for such purposeswill impart to such alloys a bright silvery luster when polished. I havedetermined that all of the desirable characteristics in an alloyintended for use in denture castings are realized by the followingformulation in approximately percentages by weight:

Percent Chromium 32 Cobalt 62 Molybdenum 5 Silicon 0.3 5 Carbon 0.3 5Copper 0.04 Gallium 0.02

In the above designated specific composition, tungsten may besubstituted in whole or in part for molybdenum and the presence ofcopper is optional.

In preparing the alloy of the present invention it is preferable to addthe gallium together with the copper in the liquid state to the moltenstainless steel or to the molten denture casting alloy. Just how thegallium reacts or mixes with the molten compositions to which it isadded is not known, but presumably it so combines with the constituentsof the alloys to which it is added as to eliminate discontinuities inthe surface of the alloy when highly polished. As the percentage ofgallium in denture casting alloys is increased, the melting point of thealloy progressively decreases. The presence of 10% gallium in a denturecasting alloy as disclosed in my prior US. Patent No. 2,128,847 wouldreduce the melting point of the alloy so that it could be cast inplasterbound refractory material and thereby reduce the cost of materialhandling and would make for simplicity of the casting operation.

Although I have described the concept underlying the invention byreference to the applicability of the concept to stainless ferrousalloys containing from 12-32% chromiurn and to non-ferrous corrosionresistant alloys intended for use in the manufacture of cast denturesand have given but a singl example of a specific alloy coma 2 position,it is to be understood that the invention is to be construed within thescope of the appended claims.

What I claim is: 1. A stainless corrosion resistant alloy comprising thefollowing constituents in approximately the following percentages byweight:

Percent Chromium 32 Cobalt 62 Molybdenum 5 Silicon 0.35 Carbon 0.35Gallium 0.02

said alloy possessing ease of flow at casting temperatures, a brightsilvery luster when polished and a resiliency essential in castdentures.

2. A stainless corrosion resistant alloy comprising the followingconstituents in approximately the following percentages by weight:

Percent Chromium 32 Cobalt 62 Molybdenum 5 Silicon 0.3 5 Carbon 0.3 5Copper 0.04 Gallium 0.02

said al-loy possessing ease of How at casting temperatures, a brightsilvery luster when polished and a resiliency essential in castdentures.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,134,670 May26 1964 Emil M. Prosen It is hereby certified that error appears intheabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 1, line 45, after "specific" insert object same line, for"invention, not" read invention is column 4, line 15, list of referencescited, for "Mar. 25, 1937" read May 25 1937 Signed and sealed this 13thday of October 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A STAINLESS CORROSION RESISTANT ALLOY COMPRISING THE FOLLOWINGCONSTITUENTS IN APPROXIMATELY THE FOLLOWING PERCENTAGES BY WEIGHT: